Soybean phospholipids have been used as emulsifiers in various oil-in-water emulsions. Such soybean phospholipids are particularly useful for the emulsification of soybean oil and similar vegetable oils, as compared to other emulsifiers such as phospholipids derived from egg and the like, because the soybean phospholipids produce more stable emulsions of soybean oil-in-water.
Naturally occurring phopholipids can be obtained from either egg yolks or soybeans or other vegetable sources, and while there are chemical similarities among the phospholipids, in each case they consist of a mixture of chemically different phospholipids, with phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl inositol being predominant components thereof. Emulsions used for parenteral nutrition produced from soybean phospholipids could be advantageous in that they are free from cholesterol. The soybean phopholipids have an added advantage in that their fatty acid composition is more similar to that of the soybean oil used in the emulsion than that of the egg phospholipids. Similar fatty acid compositions are claimed to produce more stable emulsions. Although a number of prior art workers have advocated the use of soybean-based phospholipids as emulsifiers for oil-in-water emulsions for parenteral feeding, the emulsions prepared from soybean phospholipid emulsifiers have proved to have undesirable properties and some soybean phospholipid fraction emulsifiers have proved to be toxic for these purposes.
The present invention is based on the discovery that certain alcohol-soluble fractions of vegetable lecithin are suitable for use as emulsifiers for oil-in-water emulsions and that the resulting oil-in-water emulsion made with the alcohol-soluble fractions are well tolerated when used for parenteral nutrition.
In particular, it has been found that a non-toxic alcohol-soluble fraction of soybean phospholipids is produced by extracting soybean lecithin with alcohol, wherein the insolubles are removed from the extraction by cooling the alcohol-soluble lecithin mixture at a specific alcohol concentration to a reduced temperature followed by filtration. The resulting alcohol-soluble fraction has a markedly reduced level of toxic components found in the alcohol-insoluble fractions and which exist in the natural soybean lecithin prior to fractionation.
The alcohol-soluble fraction which finds great utility as an emulsifier for oil-in-water parenteral nutrition emulsions can be characterized to some extent by phospholipids appearing therein. It has been found that the alcohol-soluble fraction which is useful as an emulsifier has a relatively low concentration of inositol phospholipids, a relatively low concentration of phosphotidyl ethanolamine and a relatively high concentration of phosphatidyl choline. A component characterized as phosphatidic acid, containing small amounts of phosphatidyl serine (referred to hereafter as PA), shown as a peak PA on the HPLC spectra, is also removed. Moreover, it has been found that the alcohol-soluble fractions of the present invention have a reduced concentration of saturated fatty acids (i.e., C16:0 and C18:0) and an increased concentration of polyunsaturated fatty acids (i.e., C18:2). Furthermore, it has been found that the alcohol soluble fractions of the present invention have a reduced concentration of glycolipids.